SUMMARY OF THE INVENTION
The present invention relates to a drive chain and more particularly, but not exclusively to a roller-type chain.
A conventional roller chain comprises pairs of opposed inner link plates interspersed along the length of the chain by pairs of opposed outer link plates. Each outer link overlies the adjacent ends of neighbouring inner links such that an aperture at each end of the outer link is aligned with a corresponding aperture in the end of the underlying inner link plate. The inner and outer link plates are interconnected on opposite sides of the chain by means of a pin that passes through the aligned apertures on each side. The pin is fixed at each end to the opposed outer link plate but is pivotal relative to the inner link plates within a bush that extends between opposed apertures in the inner link plates.
A problem with most drive chains of this type is deterioration owing to wear in the bearing surface between the bush and the pin. In particular, the location of the bearing surface in the middle of the chain makes it difficult to seal effectively against contamination. Alternatively, when it is possible to provide effective sealing the bearing surface is generally difficult to access for maintenance or lubrication purposes.
It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.
According to the present invention there is provided a drive chain having opposed pairs of inner link plates, each inner link plate being connected to an adjacent outer link by means of at least one pin that passes through overlapping portions of the respective links, wherein each outer link has at least one bore that receives an end portion of the pin and is pivotally retained thereon, and wherein a bearing is defined between an outer surface of the pin and an inner surface of the outer link bore, characterised in that the outer link is releasably retained on the pin by means of a fixing member that is designed to be received in a corresponding recess in the outer link.
In a preferred embodiment the pin is received in a blind bore in the outer link in which case the outer link may be releasably retained on the pin by means of a fixing member that is removably housed in the outer link and is engageable in a groove or slot defined on the pin. Lateral movement of the outer link relative to the pin in the direction of the longitudinal axis of the pin is thereby prevented. Preferably the fixing member comprises a staple having legs that are releasably housed in apertures in the outer link and are engageable in the groove or slot on the pin. When the staple is not present the apertures may also be used to convey lubricant to the bearing.
Alternatively the fixing member may be provided entirely within the bore. For example, the fixing means may comprise a split collar having ends that engage in slots or groove provided in the pin and the blind bores to prevent lateral movement of the outer link relative to the pin in the direction of the longitudinal axis of the pin.
Preferably the bearing is provided with at least one seal to prevent egress of lubrication. The seal may for example be an O-ring housed in an annular groove provided in the pin or the blind bores.
The outer link is preferably cast and may have an internal reservoir for lubricant that is fed to the bearing. Alternatively lubricant may be supplied to the bearing via a grease nipple or the like.
Preferably the pin is fixedly connected to the inner link plate by means of an interference fit.